A rotational angle detector (e.g., JP62-095402A), which detects a rotational angle of an object of detection based on a magnetic field that varies according to rotation of the object of detection, is conventionally proposed. In such a rotational angle detector, a magnetism detecting element (e.g., a Hall element) is rotated relative to a magnetic field generating permanent magnet in synchronization with the rotation of the object. The rotational angle detector thus detects the rotational angle of the object based on an output signal of the magnetism detecting element. The output signal corresponds to a rotating magnetic field, which accompanies the rotation of the permanent magnet relative to the magnetism detecting element.
However, in the above rotational angle detector, inductive noise due to the rotating magnetic field overlaps with the output signal of the magnetism detecting element. The inductive noise is caused by induced electromotive force, which is generated in a circuit formed by conductive wires for transmitting the output signal when the magnetic field varies according to the rotation of the object. As a result, a detection error increases when the rotational angle detector detects the rotational angle.